1. Field of the Invention
The present invention relates to the field of semiconductor circuits, and more particularly, to the field of protecting semiconductor circuits from handling damage.
2. Background Information
Semiconductor device chips, and especially integrated circuit chips, are subject to damage during handling prior to packaging. Such integrated circuits contain many thin metallization layers exposed at the surface of the chip for subsequent connection of electrical leads during packaging and thin dielectric protective layers. These conductors and passivation layers on the chip are both subject to impairment or destruction by abrasion, scratching or contamination during handling or during the packaging process. A vast number of semiconductor die are handled mechanically one or more times between the time the wafer in which they were formed is diced into individual chips and the time the chip is finally sealed in a package, whether that package be hermetic (gas-tight) or non-hermetic (gas-permeable). Some of this mechanical handling is done by gripping the edges of the chip. In other cases, it is done by vacuum pick up of the patterned upper surface of the chip. Such mechanical handling results in a certain amount of chip damage even with the most carefully designed and cushioned handling equipment. Further, as the feature size of structures in the integrated circuits become smaller, the problem of damage increases. Contact with a technician's hand, tools and so forth, can also damage these chips because of the static charge, chemicals, oils, acids and other materials thereon.
It is old in the art to disposed a "laser guard" layer on a wafer prior to dicing the wafer into individual chips or dice using laser scribing or cutting. The purpose of this layer is to prevent hot debris from the laser cutting operation from landing on and damaging or adhering to the chips. Following dicing, the laser guard material is dissolved from the chips and carries any debris with it. A laser guard layer must be removed in order to serve its purpose of carrying the debris away. Further, if the laser guard material were left on the die, the 150.degree. C. die attach temperatures would result in it crosslinking and becoming permanently bonded to the chip or die. This would create problems because laser guard materials (and photoresists) have insufficient thermal stability to survive such processes and would degrade, outgas and so forth, are not removable after crosslinking from such heat treatment without damaging the chip and would create reliability concerns.
Where chips are packaged in accordance with the high density interconnect (HDI) structure of the general type disclosed in U.S. Pat. No. 4,783,695 entitled "Multichip Integrated Circuit Packaging Configuration and Method" by C. W. Eichelberger et al., which is incorporated herein by reference, a certain amount of force is applied to the upper surface of the chip in bonding the chip to the substrate of the packaging structure. This is a potential source of contamination and deterioration of the integrated circuits.
As the feature size of chips continues to shrink, the problem of dust and other microscopic particles disposed on the chip surface can become a significant source of damage to the chips, even in the high density interconnect structure where a layer of polyimide is bonded to the chip surface by an adhesive layer, since the polyimide layer applies a downward pressure on the dust or other particle and is subject to stretching during the bonding process in a manner which can cause the dust particle to move across the chip surface thereby scratching it.
Where a chip which has been packaged in accordance with the high density interconnect structure of U.S. Pat. No. 4,783,695, has to have the interconnect structure removed because another chip in the system is defective or because of a defective wiring structure, the surface of the chip can be subject to significant forces if the adhesive layer attaching the interconnect structure to the chip surface is not sufficiently fluid to eliminate such forces.
For all these reasons, there is a need for an improved technique for protecting semiconductor chips during pre-packaging handling.